A power supply device using a secondary battery has been used for a power supply for driving a vehicle, for example. The power supply device mentioned above is provided with a plurality of battery cells 91 each having a prismatic external form, a plurality of separators 92, a pair of bind bars 95, and a pair of end plates 94, as illustrated in an exploded perspective view in FIG. 17. Each of separators 92 is interposed between adjacent battery cells 91. Battery cells 91 and separators 92 are stacked in an alternating fashion to form battery stack 99. Both end faces of battery stack 99 in the stacking direction of battery cells 91 are respectively covered by end plates 94. Respective bind bars 95 extend along the stacking direction of battery cells 91, and are fixed to end plates 94 on both ends of battery stack 99. A typical battery cell includes a conductive external case, positive and negative electrode plates, and an electrolyte. Due to the positive and negative electrode plates and the electrolyte being sealed in the conductive external case, the external case has a potential. Therefore, the surface of the external case needs to be insulated in order to prevent unexpected electrical conduction with the adjacent secondary battery or corrosion of the external case caused by dew condensation or other factors. For example, condensed water droplets may flow toward the bottom surface of the battery cell, and therefore, the bottom surfaces of the external cases need to be insulated from one another. Meanwhile, a fastening member such as a bind bar formed by bending a metal plate may be used for maintaining a battery stack obtained by stacking battery cells into a bound state. If the fastening member is formed from a metal, a structure for preventing electrical conduction between external cases through the fastening member has been demanded.
As the insulating structure, a configuration for covering the surface of an external case by an insulating sheet formed from resin such as polyethylene terephthalate (PET) has been known, for example (see PTL 1 and PTL 2 for example). Specifically, a shrink tube that can cover the surface of the external case in close contact therewith due to heat shrinkage has been used as such an insulating sheet. However, in the configuration in which the external case is covered by the insulating sheet described above, it is necessary that the insulating sheet is covered in advance on each of the battery cells. Therefore, this configuration entails problems of poor workability and rising production cost.
In addition, in a conventional power supply device constructed by stacking battery cells, a separator is interposed between the adjacent battery cells in stacking the battery cells, and therefore, the battery cells and separators need to be stacked in an alternating fashion as being positioned. This results in a complicated assembly work, entailing a problem of being unable to achieve efficient production.